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Invisible spark

Technical help for Series one, two and three Lambrettas. Models include the Li, Li Special, TV, SX, GP, Serveta and API/SIL models

Invisible spark

Postby MickYork » Mon Apr 16, 2018 7:51 am

I fitted a new external pick up and a new DC cdi and coil.......all working fine.
I decided to add my "Old" ac ignition as back up. Stator pick-up, LT coil and cdi.
The LT coil and pick-up had been left on the scooter and never touched, the wires simply disconnected.
CDI fitted and all wires connected.
I added a HT lead and suppressor cap to the "old" ac cdi, so if i wanted to swap systems over it was merely a question of pulling one suppressor cap off the spark plug and pushing the other on.

I initially started with the old ac joy starting scooter. I swapped over to my DC system..started 1st kick. tried with the ac again but no joy. I took the spark plug out to check for spark....couldn't see one. Out of interest i swapped back to DC and checked for spark again...still couldn't see a spark ?

This was all outside on my driveway. I wheeled the scooter into my garage, shut the doors, turned off lights (pitch black). Checked again for spark on both systems, still couldn't see a spark. Put plug back in....started 1st kick ? Found the reason for not starting on AC (broken wire on pick-up crimp). Checked again for spark, couldn't see one, but started ok ?

Basically, even in pitch black, i can't see a spark, but with either system (AC or DC) but it starts fine ?

Tried 3 plugs, one brand new, one well oiled and black.

Not a massive problem as the scooter starts and runs fine but any ideas why i can't see a spark ?
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Re: Invisible spark

Postby Scooter Paul » Mon Apr 16, 2018 8:00 am

Give me a slap if this is a dumb suggestion, but are you earthing the plug when you test it? By that I mean holding the threaded portion to engine earth. Electronic systems can have a less visible spark but you should still see it in normal daylight.
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Re: Invisible spark

Postby kennystag » Mon Apr 16, 2018 10:53 am

I have the same problem with my GP, i just left it the way it is, starts and runs fine.
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Re: Invisible spark

Postby CHRIS in MARGATE » Mon Apr 16, 2018 2:20 pm

If I can't see one I use a jump lead to earth the plug to the frame.
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Re: Invisible spark

Postby MickYork » Mon Apr 16, 2018 6:25 pm

Thanks for the replies.

Yes i'm earthing it to the engine, i even used a bit of emery to clean up the casing.

Might have a play about one night and see what i can find.
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Re: Invisible spark

Postby coaster » Mon Apr 16, 2018 11:14 pm

I just got my GR240 back together, it fired up but then wouldn't start. This has an Anthony Tambs external pickup and one of his high output AC CDI's. I couldn't see a spark at the plug so like you I wheeled it inside. Still no spark so I removed the plug cap but still no spark. Eventually found a crimp shorting to earth on the CDI and then had a massive juicy spark from the the cable. SO, yes you should be able to see the spark at least in shaded light, see what you get with the cap removed and if that's ok maybe change lead/cap/plug
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Re: Invisible spark

Postby TS1-200 » Tue Apr 17, 2018 9:20 pm

Had the same thing newly built GT240 motor wheeled it outside for 1st. start, checked for spark first, nothing, blast I thought checked all connections, all good still no spark changed CDI still no spark, a bit pissed off stuck it back in the shed. Next morning came out took off new plug cap and in the dim light of the shed managed to see a spark from the end of the HT lead to the casing put plug cap and plug back on and no spark ! even though all was new, put plug back in the motor and it started 2nd kick, still a bit of a mystery, nice to hear others have had the same thing
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